1. Field of the Invention
The present invention pertains to natural or synthetic hydrocarbon oils containing additives that are used as hydraulic fluids in systems that may become contaminated with sea water, such as in ships, submarines, diving rigs, underwater hydraulic tools, and the like. In particular, the present invention pertains to a hydraulic fluid comprising a natural or synthetic hydrocarbon oil solution containing a metal sulfonate, a higher molecular weight alkyl-- or alkenyl-succinic acid or anhydride, a lower molecular weight alkyl-- or alkenyl-succinic acid or anhydride, a nonionic emulsifier, and a hindered hydrocarbyl phenol.
2. Description of the Prior Art
Hydraulic fluids which are used in such hydraulic power applications as in ships, submarines, diving rigs, underwater hydraulic tools, and the like, may become contaminated with sea water. A fluid is needed which will continue to function in these systems in the presence of sea water, for example, even up to 50 volume percent of sea water in the oil, and which will protect these systems from corrosion and deterioration caused by the sea water or the salts therein. Such fluid must form a tight sea water-in-oil emulsion, provide hydrolytic stability, oxidation resistance, protection against rust, corrosion and wear, and continue to perform as a power transmission fluid without forming sludge or varnish, when contaminated by sea water, as provided in "Military Specification -- Hydraulic Oil, Non-corrosive -- Sea Water Emulsifying," published May 24, 1972 under the code MIL-H-24430A (SHIPS).
Known compounded hydrocarbon oils used as hydraulic fluids have been unsatisfactory in their ability to form tight sea water-in-oil emulsions or have been hydrolytically unstable so that rusting, corrosion, or other damage to the hydraulic systems occurred. In particular, the hydraulic fluid described in U.S. Pat. No. 3,679,588, whose composition is similar to the composition of the present invention, does not meet all the current specifications in MIL-H-24430A (SHIPS). The hydraulic fluid of U.S. Pat. No. 3,679,588 employs the condensation product of a monoalkyl phenol, tetraethylene pentamine, and formaldehyde as an emulsifier. However, this condensation product is potentially corrosive to brass- and copper-containing materials. Therefore, the hydraulic fluid of U.S. Pat. No. 3,679,588 also contains N,N'-dimethyldithiooxamide which is a film-forming metal-deactivator and serves to protect brass against corrosion caused by the condensation product. However, N,N'-dimethyldithio-oxamide tends to cause formation of surface film which may cause sticking of valves and servo-mechanisms. Further, the N,N'-dimethyldithio-oxamide film may be removed under conditions of high wear, and the unprotected brass surface would then be exposed to the corrosive condensation product. The components of the present invention eliminate the need for both the troublesome condensation product and the N,N'-dimethyldithio-oxamide in the composition described in U.S. Pat. No. 3,679,588. The hydraulic fluid of the present invention is the only hydraulic fluid which is accepted as meeting all of the performance specifications of MIL-H-24430A (SHIPS) by the Qualified Product List Section, Department of Defense Standardization Program and Document Branch, Ship Systems Engineering and Design Department.